williams



Feb. 1956 T. w. WILLIAMS NEUTRALIZATION 0F CAVITY TYPE HIGH FREQUENCYAMPLIFIER Filed June 15, 1954 INVENTOR,

. w. WILL/AMS.

ATTORNEX United States Patent NEUTRALIZATION OF CAVITY TYPE HIGHFREQUENCY AMPLIFIER Theo W. Williams, Buffalo, N. Y., assignor to theUnited States of America as represented by the Secretary of the ArmyApplication June 15, 1954, Serial No. 438,889

2 Claims. (Cl. 179-171) This invention relates to an improved method ofneutralizing a radio-frequency amplifier of the reentrant cavity type.

Ordinarily cavity type radio-frequency amplifiers are neutralized bymeans of inductive loops or capacitive probes which feed backout-of-phase voltage from the anode to the control grid. These methodsare often cutand-try and do not readily lend themselves tocavityconstruction. Furthermore, these methods require critical adjustmentsand such adjustments are difiicult to make using loops or probes.

Accordingly, it is an object of this invention to provide an improvedneutralization scheme not subject to the above ditficulties.

In accordance with the present invention, one or more apertures or slotsare placed in the common wall of the grid and plate cavities of acoaxial cavity type radio-frequency amplifier, these apertures beingpositioned relatively close to the tube. A conductive member coaxialwith the wall is then positioned over the apertures. The member isadjustable from without thecavity so as to control the effective size ofthe apertures and thereby control the amount of out-of-phaseneutralizing energy fed from the anode cavity to the grid cavity.

The features of the invention which are believed to be novel are setforth in particularity in the appended claims. The invention itself,however, both as to its organization and method of operation, can bestbe understood by reference to the following description taken inconjunction with the accompanying drawing, in which:

Figure 1 is a cross-sectional view of a reentrant cavity typeradio-frequency amplifier;

Figure 2 is a cross-sectional view along line 2-2 of Figure 1.

Referring now to the drawing, there is shown a triode 11 comprising acathode 12, grid 13 and anode 14. An anode line 15 which forms theoutermost wall of the cavity structure is connected directly to theanode. Line 16, which forms the common grid-anode cavity wall, isconpled through dielectric rings 23 to the grid 13, and cathode line 17is coupled through dielectric ring 22 to the cathode 12. To provideout-of-phase feed back from the anode cavity 28 to the grid cavity 27, aplurality of apertures 18 are placed in the common wall 16 close to thetube 11. The effective size of the aperture openings is controllable bymeans of a conductive ring 20 positionable over the slots by means of aninsulated rod 21 which extends without the cavity structure. Means, notshown, such as a knob and gearing arrangement, may be provided forvernier control of the ring position. A ring of dielectric material 19is fastened to the conductive ring 20 so as to provide a high degree ofcapacitive coupling between ice ring 20 and wall 16. In order to tunethe cavities, plungers 25 and 26 which are adjustable axially of thelength of the cavities, are provided. The anode line 15 is grounded andthe cathode 12 is maintained at a negative potential through lead 24which is connected to B minus.

Although not shown in the drawing, it is to be understood that thetriode 11 is provided with a filament for heating the cathode thereofand that leads within line 17 are provided for supplying heater currentto the filament. Also, although not shown, means are provided forsupplying an input signal to the grid of the triode and means are alsopresent for deriving a usable output from the amplifier structure. Thelatter may comprise, for example, a loop or probe coupled into the anodecavity and, similarly, the signal input to the control grid may comprisea loop or stub coupled into the grid cavity. Finally, although notshown, a D.-C. return path is provided for the grid.

While there has been described what is at present considered a preferredembodiment of the invention, it Will be obvious to those skilled in theart that various changes and modifications may be made therein withoutdeparting from the invention, and it is aimed in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of the invention.

What is claimed is:

1. A high-frequency amplifier comprising a triode, a first conductivemember coupled to the cathode of said triode, a second conductive membercoaxial about said first member coupled to the control grid of saidtriode, a third conductive member coaxial about said second membercoupled to the anode of said triode, the space between said first andsecond members defining a first cavity resonator and the space betweensaid second and third members defining a second cavity resonator, saidsecond member being provided with a plurality of slots transverse to thelongitudinal axis and close to the end thereof to allow feed-backtherethrough of out-of-phase energy from said second resonator to saidfirst resonator for neutralizing said amplifier, a member of dielectricmaterial positioned to cover said slots, a fiat ring of conductivematerial encircling said dielectric material, a dielectric rod fastenedto said ring and extending external to said resonator for axially movingsaid ring to provide adjustment of the effective size of said slots.

2. A high-frequency amplifier comprising an electron discharge devicehaving a plurality of enclosed electrodes including an anode, a cathodeand a grid, a plurality of substantially concentric members connectedrespectively to said electrodes and defining anode-grid and grid-cathodespace resonant regions, the intermediate concentric member beingprovided with a plurality of transverse slots for feeding backout-of-phase energy from the former to the latter space resonant regionfor neutralizing said amplifier, a concentric dielectric memberpositioned to cover said slots, a cylindrical member of conductivematerial adjustably fastened to the surface of said dielectric memberand means extending externally for adjusting said last named cylindricalmember to permit variation of the eflective size of said slots.

References Cited in the file of this patent UNITED STATES PATENTS

